This invention relates to digital packet communications in a network of nodes, and, in particular, to a method used in the nodes of assigning circuit ID""s to circuits in a manner that allows compliance with existing standards (in particular, the IS-IS standard) while at the same time avoiding the existing restriction of establishing no more than 256 circuits.
IS-IS is a standard technique used today by many internet service providers (ISPs) for routing message packets among interconnected Intermediate Systems (IS) nodes (typically routers) in a communications network. The IS-IS standard is described in R. Callon, OSI ISIS Intradomain Routing Protocol, INTERNET-RFC, Internet Engineering Task Force, February 1990; R. Callon, Use of OSI ISIS for Routing in TCP/IP and Dual Environments, INTERNET-RFC, Internet Engineering Task Force, December 1990; and ISO, Information Technologyxe2x80x94Telecommunications and Information Exchange between Systemsxe2x80x94Intermediate System to Intermediate System Routing Exchange Protocol for Use in Conjunction with the Protocol for Providing the Connectionless-Mode Network Service, 1990.
The IS-IS standard, when used in the environment of multicasting or message broadcast from one point to many points, has the unfortunate restriction of supporting no more than 256 circuits (i.e., interfaces to other nodes) per IS node, and requiring each circuit to reserve a unique circuit identifier from the range between 0 and 255. Extending the IS-IS protocol to support more than 256 circuits would be very desirable, since ISPs are building networks containing more and more nodes. Note that the problem just described applies only in the broadcast environment; in the case of point to point (P2P) circuits, the IS-IS protocol specification can be violated without consequences, by permitting the use of non-unique circuit identifier values, so that the 256 circuit limitation is not a problem in that environment.
In accordance with the present invention, the number of possible circuits that can be linked to each Intermediate Systems (IS) node in a local area network (LAN) is expanded from the 256 limit set by the IS-IS standard to a larger arbitrary number. The only limitation, in accordance with the present invention, is that there can be at most 255 circuits on which a given node is a pseudonode (i.e., a node on the LAN that represents the LAN) instantiated by a node that is chosen to be a xe2x80x9cDesignated Intermediate Systemxe2x80x9d (DIS), but this limitation is unlikely to be reached in any practical network environment that is contemplated today.
The strategy of the present invention is to avoid the 255 circuit limitation imposed by the IS-IS standard by initially allowing some ambiguity, and then sacrificing a small amount of additional processing time that is needed to resolve ambiguities that turn out to be problematic. In accordance with the method of the present invention, each node is initially assigned and can use a pseudonode ID containing any arbitrary, non-zero circuit ID. This status continues until it is determined that the said node is to become a pseudonode when the node becomes a DIS on this LAN; if that happens, the arbitrary circuit ID is abandoned, and the system itself is allowed (using the IS-IS standard process) to reassign a pseudonode ID containing a circuit ID that is indeed unique on the LAN and therefore unused. If the said node has not been determined as DIS on the LAN, it continues to use the arbitrarily assigned circuit ID.